Enzyme plays an irreplaceable role in improvement of baking and flour quality because of its unique biological characteristics. Currently, the usage of enzymes in processing of flour products has become a mainstream trend.
The flour used for bread baking contains glycerol phospholipids and triglycerides. When the glycerol phospholipids were partially hydrolyzed into hemolysis glycerophospholipids and triglycerides were partially hydrolyzed into monoglycerides or diglycerides, the hemolysis glycerophospholipids, monoglycerides and/or diglycerides would work as surfactants during emulsion reaction. In addition, emulsification plays a part in strengthening the dough gluten, enhancing urgent expansion in the furnace and expanding volume, which makes the bread uniform, soft and have a better taste. Therefore, addition of enzyme which has hydrolysis activity of glycerol phospholipids and triglycerides to the flour during bread baking process would obtain effects as described above. Moreover, pigments such as lutein and carotene in flour would affect the whiteness of flour products. If an enzyme which has hydrolysis activity of triglycerides is added to the flour to degrade fat, the fat-soluble pigments would be released and then fade more easily through oxidization. As a result, the flour products would be whitened.
In previous studies, the inventors successfully screened Rhizopus chinensis CCTCC M 201021 from Luzhou-flavor liquor brewing koji, which has a high yield of lipase and cloned the lipase gene from the genome for the first time and then the recombinant strain achieved high level secretion for the lipase in Pichia pastoris (Yu Xiao-Wei et al J Mol Catal B: Enzym, 2009, 57: 304-311). The inventors also used the lipase gene as the template and obtained a series of variants with improved thermostability by directed evolution (Granted patent: CN 101974499B; Yu Xiao-Wei et al. Microbial Cell Factories, 2012, 11:102-112). Then, the lipase gene from R. chinensis was mutated by molecular biology in this invention and heat resistant variants with hydrolytic activity of triglyceride and lecithin were obtained. The variants performed better at whitening bread or other products during processing of flour products and increasing the specific volume in bread baking process. As a granted patent CN 102160562 B has disclosed, the parent lipase as an additive has improved the baking characteristics of bread baking, while the present invention provides more excellent lipase variants which could be used in processing of flour products.